1. Field of the Invention
The present invention generally relates to a new and improved technique for monitoring changes in blood glucose concentration in a tissue specimen. More particularly, this invention relates to a new and improved method and apparatus for using acoustic velocity measurements as a basis for non-invasive monitoring of blood glucose levels in individuals.
2. Description of the Prior Art
The typical procedure for determining blood glucose concentration in a diabetic or other individual is to secure a blood sample from a finger prick and apply that blood to an enzymatically mediated colorimetric strip or an electrochemical probe. Since a diabetic checking himself for glucose level must perform this procedure several times in a day, it would be desirable if the pain and annoyance of the finger prick and the inconvenience of blood handling could be avoided One obvious way to alleviate this pain and inconvenience is by non-invasive monitoring.
Most non-invasive monitoring techniques have focused on using incident radiation capable of penetrating tissue and probing the blood. Three distinct non-invasive approaches are possible optical, electrical and acoustic. All currently known approaches to non-invasive glucose measurement are either optical or electrical. The optical techniques generally use infrared radiation of a selected wavelength, typically between 890 and 2500 nm, which corresponds to the region of the optical spectrum in which the skin tissue has the highest transmittance. The less successful and relatively uncommon electrical measurements focus upon the dielectric properties of water solutions in a given frequency range, typically between 1-50 MHz. In one form or another, such methods attempt to monitor the influence of glucose or other analyte concentration upon the dielectric frequency response of either the glucose itself or the secondary effect on the water.
Although investigations have been made into the use of acoustic monitoring, past studies have been primarily directed to the differences in acoustic velocity between organs. These studies have attempted to correlate acoustic velocity changes with chronic or continuous disease states. In addition, there is a large body of medical and scientific literature pertaining to the use of acoustic absorptive and scattering properties of organs for imaging, therapeutic and even diagnostic objectives.
The following references provide a background on the use of acoustic velocity measurement for the above purposes: Ultrasonic Characterization of Blood, Vol. 2, K. Kirk Shung, Chapter 10; Ultrasonic Velocity and Attenualion in Mammalian Tissues, R. C. Chivers, R.J. Parry, Journal of the Acoustical Society of American, March 1978, pp. 940-953; Tabular Data of the Velocity and Absorption of High Frequency Sound in Mammalian Tissues, D. E. Goldman, T. F. Hueter, Journal of the Acoustical Society of America, Vol. 28, No. 1, January 1956, pp. 35-37; Determination of the Acoustical Velocity in Tissues Using an Inhomogeneous Media Model, David H. Dameron, IEEE Transactions In Sonics and Ultrasonics, Vol. SU-26, No. 2, March 1979, pp. 69-74, Frequency Decendent Ultrasonic Differentiation of Normal and Diffusely Diseased Liver, T. Lin, J. Ophir, G. Potter, Journal of the Acoustical Society of America, Vol. 82, October 1987, pp. 11-38; Ultrasonic Investigation of Solute-Solvent and Solute-Solute Interactions and Aqueous Solutions of Bases, Nucleosides and Nucleotides, Journal of Physical Chemistry, 1980, pp. 692-696, A. P. Sarvazyan, V. A. Buckin, Paul Hemmes; Detection of Nocturnal Hypoglycemia In Insulin Treated Diabetics by a Skin Temperature-Skin Conductance Meter, K. Johansen, S. Ellegaard, S. Wex, Acta Med Scand 1986, pp. 213-217; Teledyne Sleep Sentry: Evaluation In Pediatric Patients For Detection of Nocturnal Hypoglycemia. Karla A. Hansen, Stephen C. Duck, Diabetes Care, Vol. 6, No. 6, November-December 1983, pp. 597-600; An Electrocapillary Flow Meter Useable As a Quantitative Sweat Detector, Robert Alric, Robert Quatrefages, Jose Comallonga, The American Physiological Society, 1980, pp. 342-346; Recent Developments in Diagnostic Ultrasound, K. Kirk Shung, CRC Critical Reviews in Biomedical Engineering, Vol. 15, Issue 1, 1987, pp. 1-25; Scattering of Ultrasound By Blood, Ko Ping K. Shung, Rubens A. Sigelmann, John M. Reid, IEEE Transactions on Biomedical Engineering, Vol. BME-23, No. 6, November 1976, pp. 460-467.